The present invention relates generally to vehicle safety seat belt retractors, and more particularly, to constant force retractors which provide a substantially constant force to a lap or shoulder belt between the home (fully retracted) and fully extended positions.
In order to protect the occupants of a vehicle such as an automobile from injury during collision, turn-over, or excessive vehicle acceleration or deceleration, a safety belt is generally provided for each occupant of the vehicle. Each safety belt includes a shoulder belt that extends across the shoulder and chest of the occupant to protect against injury, and a lap belt that extends across the lap to retain the occupant in his seat. The lap and shoulder belts are retracted in a housing on separate reels when not in use by coil springs inside the housing. When seated, the occupant withdraws the lap and shoulder belts from the reels by grasping the exposed ends of the belts, and pulling outwardly, swinging the belts around the body for engagement with buckle elements of cooperating belt sections secured to the floorboard of the vehicle.
The spring for retracting each safety belt is typically a coil type spring that has a positive coefficient of force characteristic, i.e., the pull of the spring is proportional to spring deflection. As a result, pull on the belt tends to increase as the belt is withdrawn from the housing on the reel. The pull is minimum with belt fully retracted and is maximum with the belt fully extended.
The spring must be heavy enough to fully retract the belt into the housing so that the belt is out-of-sight when not in use. On the other hand, the pull should not be excessive with the belt fully extended because pressure against the shoulders and lap of the occupant causes discomfort. Furthermore, the belt is difficult to pay out against the increasing retracting force or pull provided by the spring. The discomfort caused by the excessive retracting force of the belt, and difficulty in payout discourage use of safety belts with accompanying increases in occupant injuries and deaths.
Accordingly, one object of the invention is to provide a safety belt retractor that exerts a pull on the belt that is constant between the fully retracted and fully extended belt positions.
In application Ser. No. 667,222, filed Mar. 16, 1976, to Schottoefer, assigned to the Assignee of the present invention, the retraction spring inside the reel housing of a safety belt retractor is continuously or stepwise tapered along the length of the spring to exert constant pull to the belt as the belt is protracted from the reel housing. While the tapered spring arrangement functions satisfactorily, the spring must be specially manufactured, and the narrow portions of the spring are somewhat prone to breakage.
An additional object of the invention, therefore, is to provide a new and improved safety belt retractor having constant retracting force that is durable and uses a standard helical coil spring.